Is it natural to use the phrase on the same level in sense of being as good at doing something as someone else? For example:
Kate and Tom are on the same level in terms of math.
Would it be better to use at instead of on there. For example:
Kate and Tom are at the same level in terms of math.
If this usage of the phrase doesn't sound natural at all, what would a native English speaker say instead?
Best Answer
Yes, the phrase is idiomatic, as Ronald Sole stated in the comments. And both versions are commonly used. Since the late 1960's, "at the same level" has been more popular in books than the other version (see the Ngram that Ronald Sole linked in the comments). "Level" means "someone's ability compared to other people" (Cambridge).
Note that the phrases are not only used to compare qualities between two people/things but also to compare the same person/thing over time.
There are other ways you can write this. In your case, you can say
or
You can also use the idiom "on (a) par with", which means "at the same level or standard as (someone or something else)" (Merriam-Webster).