Goofs

The successful laser test shoots a hole through the cinder blocks, out the lab window, and through the head of the statue on the campus lawn. Later, the statue is shown with the head intact.

During the party scene, Chris first puts a blue lei around Mitch's neck and has a red lei in his hand. In the next shot, Mitch is wearing the red lei and Chris is holding the blue lei. Then in the next shot, Mitch is wearing the blue one and Chris is once again holding the red one.

Chris' earmuffs appear and disappear in the ice skating scene.

When Chris is warning Mitch about "ending up in the steam tunnels" like Lazlo, Mitch is holding a pile of laundry. In some shots it is a plaid shirt in his hands, in others a bright yellow blanket.

When Chris is excited about possibly figuring out the solution to the laser's power problem in the break room, he leans into the snack machine and jumps up and kicks the freezer door, knocking off the shelf bar. In the next shot the shelf bar is back in place.

As anyone who has ever made microwave popcorn (which is essentially what is happening at Hathaway's house) knows, the process releases a lot of steam, which is what drives the popping. As a result of that, Kent would have at least been severely burned just from the steam, if not cooked alive if he didn't get out of the house in time.

The laser that Knight finally gets to work supposedly works at 600 nanometers. Unfortunately, that would make it an orange laser, not a violet one as shown in the film (which would have a wavelength closer to 400 nanometers).

In the end credits, the name of the Hewlett-Packard company is misspelled as "Hewlitt-Packard".

During the laser test, the range controller clears the B-1 to Flight Level Six-Five-Zero, which is 65,000 feet. The service ceiling, i.e. the highest altitude the B-1 can attain, is around 40,000 feet, and it has never flown above that altitude. However, 65,000 feet was an erroneous altitude, because the outside shot of the aircraft shows that it is flying at low level, just over the mountains and the desert floor is visible. This would not have been the case at 65,000 feet.

The false IDs used by Chris and Mitch to enter March AFB are shown as DD Form 2A - which is an identification card for military personnel (one of them is shown to have a pay grade of "O-1" - for the Air Force, that's a Second Lieutenant). Chris tells the gate guard that "Someday you might be in the private sector, too" - but if they're covered as military officers, they're not "private sector" personnel. With a DD2A, they'd also have had an easier time getting through the gate in uniform, rather than in civvies.

They say the ice in the hall would sublimate directly to gas. If that would be true, it would be impossible to skate or glide on this kind of ice as the building of water is essential for gliding/skidding on ice. However, Ick never reveals what the substance is, and it's possible his mystery substance can both sublime and provide for skating.

When Mitch finds Lazlo's hidden lab, we see Dunkin Donuts boxes and bags strewn about. The film setting is the fictitious "Pacific Tech" university, which is portrayed as a Southern California school similar to CalTech. Dunkin' Donuts locations did not open in California until 2014. Actually, Dunkin Donuts existed in Southern California until the late 1990s, then was reintroduced in 2014. Furthermore, this isn't a period piece, so all depictions should be accurate as of the filming of the movie.

For Lazlo to mail in 1,650,000 entries into the Frito-Lay sweepstakes with $0.20 stamps would cost him $300,000. This would far exceed the value of any and all prizes he would get even including the car. Actually the cost of mailing a post card in 1985 was 13 and later 14 cents, so at worst the cost would actually be $231,000; still a lot but more accurate to the time.

They speak of increasing laser output by "an order of magnitude" to 6 megawatts. While they are currently at 5 MW, the increase referred to an earlier model which was presumably operating at around .6 MW.

When Jordan brings Chris and Mitch the fake IDs to get into the military base she first gives the wrong one to each of them before switching them. As Chris Knight is looking at his he flips it over to another picture of him, but the name on the top is that of Mitch Taylor. Jordan gave them the wrong badges because she accidentally mixed up which picture went on which badge.

When Mitch finally cracks and calls his parents to come home, Kent and his friends decide to record the call as a joke. Later when the call is played over the PA in the cafeteria, it includes the first 10-20 seconds of the call, which would not have been included as that was when Kent and them went to start recording it.

Following the laser shot the side of Jerry's house should at the very least be scorched if not actively in flames, yet other than the broken window there is no visible damage.

When Kent rolls out of the front door with the popcorn, it is obviously a stunt double due to the man's hair being brown/black and Kent having blond hair.

When the front door of Jerry's house is burst open from the popcorn joke, popcorn is already visible on the porch next to the door. In this scene, new popcorn falls into the exact same position (indicating previous takes).

Dr. Hathaway is shown wearing a wedding ring despite his character being single. This is a common technique among unmarried people who appear regularly on television (as Hathaway does). Wearing a wedding ring can help deter and discourage stalkers who might otherwise harbor unwelcome romantic interest toward a television personality.

The trajectory of the final laser makes no sense. It's fired parallel to the ground about three or four feet off the ground, but when they follow the path of the laser onto campus and into town, the path goes much higher, as if it bent, but there was no cause for it to do so.

Chris does say "If you want to leave", but silently mouths "No way", then he says "Go ahead". No audio/visual mismatch occurred...

Reflected in the bathroom mirror.

When Mitch discovers the secret passage to Lazlo's hideout, it is after Lazlo went into it and disappeared. As Mitch opens the panel to find it, a car is there to take him to it. Problem is, there's only one track and one car. Also, the amount of time it takes the car to travel to it is so long that even if Lazlo sent the car back (which would be the only reason the car would be there after he went down there and a highly unlikely thing if he's technically the only one who knows about it or is the only one who goes there) it wouldn't return so fast as to be there for Mitch to see and get into, considering he found the passage only mere minutes after Lazlo went that way.

Given that Lazlo was still mailing contest entries just before Chris' final exam, and that the crossbow test was likely within days of that exam, it doesn't seem plausible for Lazlo to pull up to the test aftermath with all his contest prizes. There wouldn't even be time for the aforementioned batch of entries to arrive at the company and be processed before the test! In reality, it would probably be several months between the end of the contest and the arrival of any winnings. Additionally, prizes from different manufacturers would likely be shipped separately, and at different times.

When Hathaway first goes into the laser lab and exchanges conversation with Kent and the others, you can see the shadow of the overhead mic swinging back and forth. The shadow appears faintly on the far wall.

At the science fair, on the poster for "Alcoholic Mice," the word "laboratory" is misspelled.

Dr. Hathaway is wearing a wedding ring even though he is single.

Kent picks up popcorn off the floor and eats a piece, exclaiming, "Popcorn!" In addition to it very obviously appearing to be popcorn, people with braces (as Kent has) are not allowed to eat popcorn as it can damage the wiring. Kent, being an obvious stickler for rules, would know this.