Not sure if I'm the first to find these. Probably not.
These were done with the Wii version, But they're likely to work with any other version. Maybe.
:: Bike Nitro ::
When pedaling as fast as possible if you suddenly hit the brakes and quickly resume pedaling, You seem to gain a temporary speed boost.
This is useful as if you buy an Aquaberry Bike use said trick, It seems to be just as fast as the best BMX(?) bike you can get from Shop Class. Minus Jumping though.
:: Bunny Hopping ::
As you likely know, The fastest you can go on foot is by rapidly hitting the Run Button. That's (a) on the Wii.
However if you intersperse Two Jumps in quick succession and finish it off with more dashing, then jumping, then dashing, etc.
You can cover much more ground. However once you get the Skateboard, There really isn't much reason to use this trick..
However in a Speed Run it would be useful for the first piece of the game.
:: Heaaaaadshot! ::
You probably already know that if you Egg someone's face, it will stun them for a few seconds.
Did you know if you shoot them with a fully charged slingshot, or any weapon at all, it does double damage?
:: The Time Warp ::
It's astounding, This trick allows you to warp to the start of the next school day.
If you get busted near the time you would pass out, You may get warped to the next day instead of your bed.
Where you get warped depends on who caught you, Outside school it'll be the School Entrance.
Inside school it'll be in front of the Principal's Office. It may be possible to get detention by using this trick.
If anyone knows any other tricks, Go ahead and post them.
edit: Added in the "Heaaaaadshot!" trick.
