Amanda Bynes -- Kicked Out of Fashion School for Weed, Bizarre Conduct

Amanda Bynes was out of control at her fashion school ... showing up high and offering fellow students money to do her homework ... and we're told it got so bad she was kicked out.

Several classmates at the Fashion Institute of Design and Merchandising in Irvine say Amanda has shown big signs of trouble for a while ... and various people have told us she often went to class high on weed.

Student Rachel Loritz tells TMZ ... Amanda often ditched classes ... but even when she showed up, she was clearly high, and not good at hiding it ... she almost always wore sunglasses and laughed out loud at inappropriate times.

We're told the pendulum would often swing and she would then get in "horrendous arguments."

Rachel says ... Amanda paid fellow students to do her homework ... and some took her up on it. Rachel says she rejected Amanda's offer.

We're told Amanda was caught cheating off someone during a test ... and when she was called out she threw a fit.