The numbers do not bear out the contention. One school related attack ocurred in 64,66 and 71. None in 72, 73. two occurred in both 74 and 75, but it went back to zero in 76-81, dropped to 1 a year in 82-84 and to zero in 85-88. Between 89 and 94 there were four total attacks. If a new pattern emerged at any point it was in 98. SInce 98, there have been 9 years with three or more attacks.
No matter what you think, the change can't be correlated with Roe v. Wade.