In a classroom scene, Mr. Sharp writes on the blackboard "all men are created equal." He asks the class "who wrote that?" The class jokes "you did." Then Sharp says it was 'A. Lincoln'. It was written by Thomas Jefferson in the Declaration of Independence.
When Nina Joey and Richie go to the party, My Boyfriend's Back by the Angels is playing on the record player. The Angels were on the Smash label which was all red, the record playing was on a green label, Lucky Seven records.
The Fordham Baldies are portrayed as bald. The real "Baldies" were in fact named for the American Bald Eagle, and the gang sported elaborate "D.A." hairstyles. Dion DiMucci was a member as a teenager, and he alludes to this mistake in his autobiography, The Wanderer.
The Holy Mass/Holy Communion scene with the Duckies has several factual mistakes. First, before Vatican Council II in the late 1960's, evening Masses were extremely rare, usually taking place only at the Easter and Christmas Vigil Masses. In the movie, 25 candles are burning. At most 7 candles would be lit on or near the altar during the celebration of the Mass. The priest is throwing the host into the recipients' mouths when in real life he would have been gently placing them on their tongues. The movie includes a potato chip crunch sound. Being made only of wheat and water the hosts are silent when chewed. Finally when the one Duckie goes to investigate the screams of Turkey, he genuflects towards the altar on his left knee. In reality one always genuflects on their right knee. The people responsible for this should have done a better job.
Perry and his friends are driving after Nina, when they get lost and are found to be in the place of the Ducky Boys. After that, Perry goes out from his car to fight with them, when one of the Ducky Boys hit him with a baseball club until it breaks up. When the same guy is seen again in a different scenery, the baseball club is back to normal.