"I will go to high school next year."
Are you asking whether "會"(T.C.)/"会"(S.C.) should be added?
There is nothing wrong of the sentence "我明年會上高中" or "我明年上高中". Both have the same meanings.
You can think that "會" here is just to let you know it's talking about the future.
Different from English, Chinese verbs have no tense. Chinese has no strict rules to add "會" before verbs when presenting future actions.
Therefore, if the sentence has already mentioned the time (here is "明年"), it's nothing matter to have 會 or not as we already know it's talking about the future.