grammar - What does 通る mean in this context?

This is an excerpt from a conversation with my language partner:

息子は明日から冬休みです。 絵画教室に通っているので、冬休みの間は、[写実力強化講座]{しゃじつりょくきょうかこうざ} (realistic painting workshop) に行きます。

My attempt at translation:

"From Sunday on, my sun has winter vacation. Because he passes through a drawing-class (course?), during the winter vacation, he goes to a 'realistic painting workshop intensifying course'."

This is a minor issue I have here. According to jisho.org, 通る means "to pass through" and a lot more. I think to pass through fits the context best because her son seems to partake in drawinglessons which further his skills in drawing. However, I'm also a bit irritated by the use of 教室 and 強化 . I think 教室 refers to the regular lessons at obligatory school education here? That's why I am a bit confused, because it sounds like these lessons in drawing are a temporary thing at school for which he receives extra private lessons during this winter vacation. Here in germany, we have drawing lessons from the beginning to the end of our obligatory school education (although these lessons are, to be honest, a joke^^). So there is nothing to "pass through" since these lessons/classes are there the entire time of our school education :D Thats why I wonder wether I interpreted 教室 correctly or not.^^

Answer

「 息子{むすこ}は明日{あす}から冬休{ふゆやす}みです。 絵画教室{かいがきょうしつ}に通{かよ}っているので、冬休みの間{あいだ}は、写実力強化講座{しゃじつりょくきょうかこうざ} (realistic painting workshop) に行{い}きます。」

Your translation attempt is:

"From Sunday on, my sun has wintervacation. Because he passes through a drawing-class (course?), during the wintervacation, he goes to a 'realistic painting workshop intensifying course'."

First of all, in this context,「通って」 is read 「かよって」 and not 「とおって」. That is 「通{かよ}う」 vs. 「通{とお}る」, two different verbs.

「～～に/へ通う」 means "to commute", "to attend (school)", "to go (someplace) on a regular basis", etc. 「～～を通る」 means as you stated.

Next, 「教室」..

In the context of "regular" schools such as elementary, junior high, high school and college, the word refers to each physical "classroom".

In this context, however, 「教室」 would refer to an after-school type of school or perhaps a cram school for students wanting to get into an art college in the future. (I, for example, attended the そろばん教室 (abacus school) and 書道{しょどう}教室 (brush calligraphy school) as a kid in addition to regular school, that is.)

Thus, 「絵画教室」 is a drawing/painting school. For translation purposes, one could use "class" or "course" as well.

「強化」 here would simply mean that the course is intensive in nature, which is made possible during the long recesses at the "regular" school.

Finally, there is no "Sunday" mentioned in the original. It must have been a mental mistake.