Yes, you can. The sentence pattern is as follows: 因为 A 所以 B = because A therefore B 因为我去一座寄宿学校, 所以我可以做五花八门的课外活动。

yes, 因为...所以...

Technically, that sentence is right. But we Chinese don't always state reason after "因为", but we have to add "所以" before the results. It would sound more natual to drop the “因为”. So that sentense would be "我去一所寄宿学校，所以我可以做五花八门的课外活动"