Being able to do a plie exercise without the barre, without straining in your neck and shoulders, and with being on balance throughout, tells you that you have developed strength.
Standing in coup de pied, hands on hips, and being able to slowly press up to demi pointe, and lower slowly, 4-8 times, tells you that your postural plumb line is maintained, and that your ankles and arch have developed strength.
Again, assuming that there is no strain in the upper body, or loss of turnout.
Doing an echappe to seconde on count 1 hold 2 hold 3, close on 4, 8 times, with posture, turnout and arches held, neck and shoulders easy, tells you that you have built strength in your core, legs, and feet.
But what if you can't do the above ballet exercises? What are the basics that you go back to in order to build strength? Practising at home is good, although you need to be sure that you are doing the right thing over and over, and not repeating incorrect technique.
How do you fit extra practice in along with school homework and some "normal life"? Well, foot exercises, turnout exercises, stomach and waist exercises, can all be done while you're watching a movie or studying.
You can do a great psoas stretch while sitting on a physio ball in front of your computer.
Stretch one leg behind you, with the ball of your foot on the floor, and gently straighten the knee and hold your posture upright.
And keep typing! Or reading..
you'll stretch your hip flexors too.
Pause and do a small easy backbend to get that little extra.
There is a wealth of information available now for serious students.
Use it to set realistic goals.
Don't waste time wondering when all your questions can be answered!