Sharon:

I have not done much research in this area, but I can speak from my experience with today's students, who like content that is current and learning activities that are highly interactive relating to topical issues based on their prior reading/experience/ local or societal issue. So, I don't think "motivation" necessarily builds over time. I presented at last year's Scholarship of Teaching and Learning conference in Indiana, U.S. with the theme on "motivation" for both students and teachers. I hope that the attached can be helpful in answering your question.

Many thanks,

DFJ.

Conference Paper Debating: A Dynamic Teaching Strategy for Motivating Student...

Hi Sharon, here is a good paper that studies intrinsic motivation from childhood through late adolescence.  In my career as a teacher, I do my best to strengthen intrinsic motivation, being fully aware that in my country, students are usually extrinsically motivated  by grades; and it is intrinsic motivation that develops scholars and scientists whose minds are close to their work.  

Yes, I have come across several students who make great strides in motivation to study!  Have a look at this paper.  All the best.

Article Continuity of Academic Intrinsic Motivation From Childhood T...

Thanks so much. I will.

Kind regards, Sharon