First things first: decide what it is you wish to teach your students.
- fundamental exposure to robot technology
- simple programming via Teach Pendant Programming TPP
- more complex programming with structured language
- simple pick & place or more complex path applications
- systems integration (sensors, grippers, vision systems...)
Simple: less time, effort, cost. Students get less learning and skills.
Complex: more time, effort, cost. Students get more skills (but is more needed for High School?)
Do your students already have some programming experience? Many do not. Nor have patience to read, study, and learn.
My University / Engineering Technology labs use small Kawasaki units. Selected because of TPP +AND+ a very powerful & easy structured language together. Not terrible. But I only use TPP because my students are iPhone generation and don't know, and don't care, about structured language programming.
I use RoboDK extensively in my course. I want students to know what is offline programming and also to help visualize 6DOF motion. Education license is what I have, minimal or no charge. Full function, six months. RDK is a very good package once you get over the learning curve. Can integrate Python programs for exotic actions, so can do "programming" with that.
I wanted to evaluate an interesting new small lab scale 6-axis cobot from IGUS. But these products are new release this past Spring and I have not been able to get my hands on one yet. I ***think*** I got budgetary pricing of ~USD$9K (?) each at one time. They also have other types like gantry units.
Skyefire mentioned Automation Studio. Fabulous product, insanely expensive for Academic use. I discovered a much less expensive alternative that I use in my classes, AUTOSIM PREMIUM from IRAI France. Less polished than AutoStudio or the equivalent FESTO software package, but very powerful anyway. I use it to teach students fundamentals of pneumatic circuits. My colleague uses it for hydraulics technology. It can also be used for PLC and industrial control circuit simulation.
IRAI France also has an interesting "robot" simulator package for HighSchool or less called MIRANDA. You may find this interesting. Find link to it on their website.