Relationships and portals 2- UGH!

After following the threads and also receiving excellent help on this forum, I am one piece short and pulling my hair out - and I'm no spring chicken!

I have 5 tables: Students, Assets, Transaction line items, transactions in, transactions out... The purpose is to allow students to checkout and return equipment and keep track of it.

I may have done this wrong... but you can see the relationships. Everything seems to be working except (and this is where my thinking may be WAY OFF)... the checkin area. Is it wise to have two different tables - one for check outs and one for check ins?

The checkout area works fine... I can enter a student ID and get the related info and then add items. I can even go to the checkin area... enter the checkout transaction number and it will pull that data to checkin.. However, students will not always checkin ALL of the items they originally checked out at the same time.

What I am hoping to do is to create a checkin layout that will allow me to enter a student ID (instead of a transaction number) and only have the portal show checked out items in a new record (in the transaction in table)... This way I can assign a checkin transaction number each time they checkin materials regardless of the checkout transaction

Am I thinking this correctly?

CheckOUT.1.0.2_rev.fp7.zip