Practice it at home, 2-3x per day.
Sit in a straddle, wider than a right angle or 90 degrees. Now lean forward while putting your hands right in front of you. Lift your heels up as high as possible and practice holding for 10 seconds. Do this 5x
In the same position, do heel lifts in sets of 5 or 10 about 5x. You can increase the number but I am prescribing numbers that are very beginnerish. Another good exercise is to do rotational circles in 5, 10, or 20 forward and backward. Couple sets.
Practice the straddle lever at home. Find something high like sitting in a chair or straddling a bench. Practice at least 10-15x.
It will hurt, adjust how many times by how much it hurts. Morning and night minimum with possibly once when getting home after school and another time in the evening.
Just like a handstand, it's a matter of practice and stretching out hip flexors and making them strong. Make sure to work pike stretches to work on your hamstring flexibility.