Many of the main characters are named after famous scientists. William Bradford Shockley (1910 - 1989) was an American physicist and inventor who won the Nobel prize in 1953. Dr. Robert H. Goddard (1882 - 1945) was a pioneer in the field of rocket science. Otto Hahn (1879 - 1968) is a German chemist who is credited with the discovery of nuclear fission. The Meitner School itself is named for Hahn's colleague, Swedish chemist Lise Meitner (1878 - 1968).
When his father asks Shawn how a 30 year old could pass as a Teenager, Shawn tells him that with a wig, Henry would look like he did when Shawn was a little kid, referring to the Flashbacks where Henry uses a wig to look younger.
The trivia item below may give away important plot points.
Shawn makes mention of how them going undercover at the high school is like 21 Jump Street (1987). The character of Kirk Godel/Jay Macendale, who is in disguise as a high school student, is played by Shane Meier who actually was on "21 Jump Street."