Hands-on quite literally means having students 'manipulate' the things they are studying - plants, rocks, insects, water, magnetic fields - and 'handle' scientific instruments - rulers, balances, test tubes, thermometers, microscopes, telescopes, cameras, meters, calculators.
(they; are studying; - plants, rocks, insects, water, magnetic fields)
they
are studying
- plants, rocks, insects, water, magnetic fields