Well implementing xAPI is certainly an option and would give you an immense amount of flexibility in terms of what you could report on. Note that Adapt doesn't have support for xAPI yet, it's something we're focussing on this year. There are some community plugins that provide xAPI support.
However, leaving xAPI aside, f you just want to record a score that's pretty easy, particularly If you can uniquely identify the user on the server side so don't have to worry about passing a user id into Adapt and back out again.
Have a look at how the assessmentResults component works as a starting point - that demonstrates code that listens for when an assessment is completed and then extracts all the necessary data like the score from it.