Introduce memory and efficiency a few months into the AP CS course. Do so in a hands-on way by demonstrating how a computer cannot compute a slow problem.
When you write a function, like (foo x), students don’t realize you can put a variable with a name OTHER than x in there, or an actual number.
Teach students that running tests cannot prove that a code works. It can, however, prove that code is not working.
When creating websites, many misconceptions students have arise from not fully understanding CSS, Cascading Style Sheets.
Emphasize that students should know which HTML tags are self-contained to make writing and debugging code easier.
Emphasize that it is not necessary to add the reference operator, &, in C++ when passing an argument to a function that takes in a reference.
Emphasize to your students that in languages like Java a semicolon ends a complete thought, rather than just a line of code.