It's about a happy kid on his/her way to school and s/he felt happy because s/he was going to bomb the school today the s/he succeed. "The teachers are not aware of it". It is a well-known song.As Chenyang explained, the original version is 《上学歌》. This version is called 《炸学校》.Someone believes the adapted version can date back to 1990! .I heard it around 2003-2005.

不知道你指哪一首

Sometimes kids change some lyrics of classical songs. Some are not suitable to learn, but just for fun.

Hehe, I searched it from baidu, maybe this is what your are looking for: 太阳当空照，花儿对我笑，小鸟说早早早，你为什么背着炸药包，我去炸学校，老师不知道，一拉弦我就跑，轰的一声学校不见了。 It is reedited by this song:《上学歌》 太阳当空照，花儿对我笑 ，小鸟说早早早，你为什么背上小书包 ，我去上学校，天天不迟到，爱学习爱劳动，长大要为人民立功劳 。 Hope my answer can help you :)