Tense Consistency and Conditional Verb tense

I had just told someone that someone couldn’t join our study group because he didn’t have a good enough foundation.

As a reply, someone wished to say, "If he joins / joined our study group, he would get better at English as time goes / went on."

My real question is on the last half. Should it be "goes on" or "went on." I know "would" has many uses other than it’s ability to express the past tense, but I am unsure if it is always necessary to keep accompanying verbs in the past tense as well.

Thank you.