As long as all the students' various sections are all related to each other by means of a common reference point (preferably located at the origin) you should be able to import/reload them as Gaius suggests...or even open each individual one to check it over, then select and copy it. Then Paste in Place in the master model file.
That common reference point can be created by starting with a single, coherent base model, as Gaius suggests or, if you really want to test their accuracy, by getting them to model their sections from scratch, located by careful trigonometry.