A word to describe an unexpected advancement in someone's learning progress

How to describe an unexpected or surprising advancement in someone's learning progress?

For example, in one teacher's class there are some students who were quite lazy in the first semester, but suddenly became extremely enthusiastic in the middle of the second semester. However, this sudden change did not happen with all the students. So, say, Jack is one of such "no-sudden-change" students. However, Jack was not at all a bad student. So, the teacher is writing in Jack's progress report in the end of the second semester:

Although Jack hasn't shown any surprising upsurge in his learning progress as was the case with quite a few other students in this class during this semester, he has nevertheless been quite diligent and active.

I guess the word "upsurge" wouldn't fit in here as, as I perceive, it is usually used in reference to many people (like "upsurge in sales"), rather than to one person.

"Advancement" would probably not work here either as advancement, as far as I understand, implies a more steady process rather than a sudden one.

So, what word would fit in here then?

... Jack hasn't shown any unexpected breakthrough in his learning progress ... Or, ... Jack's progress hasn't made an unusually significant advance in his learning progress as was the case ... Or, more formally, ... Jack hasn't achieved the notable large increase in his learning progress ...

One way to describe it would be by using "improving by leaps and bounds".

By leaps and bounds (link to Collins dictionary)

  with unexpectedly rapid progess 

E.g. "her condition improved by leaps and bounds"