Steal your victim's cell phone and tape it under a desk or chair, or hide it somewhere they'll never find it. then start calling them while keeping your phone hidden.
Duct tape your friends legs while he is asleep. but be careful that there isn't any sharp-edged object near him, which can cause some injury!
Tie one end of a spool of ribbon to your victims doorknob with a note stating, "follow the ribbon." then wind the ribbon all around their room, bed, desk, even all over the house. at the ending point of , attach a note "so finally you joined the fools league!"
Draw moustaches on the face of the person whom you know is a sound-sleeper. use an eyebrow pencil or other make-up. no markers please, they're too hard to remove!!
Block door with a see through plastic wrap. then wait and watch who gets bounced back on opening the door.
swap the phones of the victims who own similar makes and models but keep them in different color cases, giving each person back the correct case, but the wrong phone!
record the morning news telecast of the rainy day when schools were closed due to heavy downpour/snow. then play it back on april 1st in the morning while the kids are getting ready for school.
Put a small amount of paint or ink on your finger. go up to your victim and pretend to notice a "mark" on the victim's face. tell the victim that you'll rub it off. instead, actually place a mark on their face. act like you got the mark off and walk away.
Find a small picture of a a funny creature (monkey, donkey, baboon, etc) and use a glue stick to place it over the photo on victim's driver's license. then send him out for beer, or have some better excuse to send them somewhere where they need to show their id.
prepare a special sandwich for the victim. but don't remove the wrapper from the slice of cheese. when they bite down the victim'll get a chewy surprise.
stuff victim's shoes with some cotton, when the person will try wearing it they will feel that either their feet have swollen or the shoe has shrank.
Right before a lecture as you are walking into the classroom, ask one of your classmates if they are "ready for the test today?" involve one more pal of yours in the prank who can authenticate your statement that there is indeed a test that day.