As everyone else has said, grammatically correct, but sounds wrong. Defn not one to pick up on (unles you want to get into a debate on the relative values of 'correct' vs colloquial grammitical constructions
Wow-that was fast.I see what you mean,but it just sounded odd.ie 'James was learning about recycling',singular,sounds right,but 'class 2d was' doesn't. Thankyou-I shan't go in and flaunt my ignorance now.
Contentious one this. David Crystal (top lignuistic scholar) says there is a case for using either 'was' or 'were' depending on whether you want to show the entity as being absolutely as one, integrated, or with the potential for divergence - i.e. 'The government is totally in agreement on this issue', vs. 'The government are in disarray'. So the class would usually be a singular entity but with certain statements using the plural would be appropriate. So no, I think it's fine and wouldn't mention it. Save that for a wrongly used apostrophe!
'The class was learning' is technically correct, because there is one class and so it is/was learning. But because the class is composed of several/many children, it is acceptable - but less correct, as such - to say that the class are/were learning.
If you complain to the teacher, there is, I fear, a risk of norkdom. If you want the full force of MN judgment, take this over to Pedants' Corner!