Most efficient method of adding new data columns to PowerQuery

[PowerBO]

Every week at school we run an attendance report. 

Our reason for using Power Query is the match the attendance percentages with the pupils through PQ's data merge feature. We have pupils arriving and leaving, and this makes the job easier (perhaps there is an alternate solution?).

In any case, as the weeks progress, this merge needs to take place again and again, adding new attendance percentages for each new week. 

At present, my method is to import each new attendance report as a new query, then merge it with the existing one. 

This doesn't sound like the most arduous task, of course, but we have some specific formatting settings that don't carry over. Additionally, it's something we do with a whole host of other pieces of data, not just attendance. Thus, optimistically, I wondered if anyone here had a method for doing this more efficiently.

If not, then I'm still grateful for how quick this is versus the manual method other staff members were using (yikes). 

Thanks for your time and any help.

[PowerBO]

Dear Pat,

Forgive me for not replying sooner. 

Not sure how to host a file for download for you. 

I've included snapshots as a compromise.

[ppm1]

It sounds like there should be a much more efficient way to do this. Can you provide a link to sample data/files with mock data? That will help you get a specific solution. I'm also curious why you are bringing in attendance percentages. Usually the raw data (present/absent) is brought in and that is calculated with DAX in your report.

Pat