"我明年上高中。"

Translation: I will go to high school next year.

[LawsonBaxt]

"will" isn't really needed in the English

[tsunbae]

I'm surprised none of these are also offered (in contracted and long forms)
Next year, I'll be in high school.
Next year, I'll be attending high school.
I'll be in high school next year.
I'll be attending high school next year.

[RajasDaithankar]

@Tsunbee - I'm going to be in high school next year. Next year I'm going to be in high school.
I'm going to attend high school next year. Next year I'm going to attend high school. Next year I will move to high school. I will move to high school next year. Next year I'm going to move to high school. I'm going to go to high school next year. Next year I'm going to go to high school. A year from now I will be in high school. I will be in high school a year from now. I'll attend high school a year from now. A year from now I'll attend high school.............
And another twenty dozen variants based on whatever one fancies.

[Juliet730073]

"Next year I will be in high school" should be accepted

[DesmondAllen]

i start high school next year

[mikey_dredz]

Or "I'm starting high school next year". I don't think "上" specifically has to translate as "to go", but Duolingo only accepts that translation.

[Ni4yu]

Why is not allowed "be going to"?

[StephanusG1]

It's also possible. Report it.

[Haruka748933]

How about " New year I will enter high school"?