Were you taught using 人教版 or 北师大版 history textbook? I'm pretty sure 四人帮 and 大跃进 were inside 北师大版 and called a mistake. Well at least for my year. Maybe they changed it, or you didn't pay attention in class.
It was quite a while ago so I don’t recall who made the book, I went to high school there more than 10 years ago. I used whichever books were standard. But if I remember correctly, they portraited Si Ren Bang as a group of four planning against the state, no fault was assigned to China or Mao.