Hello Richard, the free plan is still an option and it would allow your students to discover Glide and how to build with no-code. Though they would be able to preview their apps in the layout editor, they would not be able to publish their work.
Should you need to review their work as their teacher, you could ask them to publish their app as a template and share it with you that way. Using the template feature is how editors on free accounts share their work with other editors.