Since I rode horses for a long time before I skated, I had only heard the term 'check' in a horse related discussion. In a simplified description, in riding it means get your seat down in the saddle, and close your fingers on the reins. This 'checks' the horse without bringing to a stop, it causes the horse to shorten its stride as it approaches a jump so it takes off at the right point. The whole 'checking the turn' was a foreign language to me.
To this day I think that 'checking the turn' is harder for adults to learn than it looks. At least it was for this particular adult. I don't know how various coaches introduce turn checking. I've had the swivel hips and shoulders lesson, the many demonstrations, none of them worked for me intuitively.
What I needed was practice. And there's just so much time you can spend on ice practicing 3 turns if they give you trouble. But I've found a way.
Let me introduce my 3 turn checking training device, for sale nationwide. Ladies and gentlemen, the paper plate.
I used the ones that are paper with the waxy finish
Step 1: Put feet in boots, lace them up like they're your skates. I used a pair of old jodhpur boots with a slight heel. I wanted something that gave me a feel of skates, with a similar heel.
Step 2: Put plate on floor.
Step 3: Put boot on plate.
Step 4: Do a 3 turn.
It's that simple. I would just leave the plate on the kitchen floor and do 3 turns every time I went through the kitchen. At first I could get the turn but would wobble and not be able to hold it coming out of the turn. Being at home I could try various arm positions and timing. I could look at 3 turn videos and follow the instructions. I could remember my coach's instructions and practice them. Eventually, I got everything to come together and my 3 turns on ice improved. But because I had off-ice practice at home, I really got comfortable with the moves in an environment where a fall was not going to happen. When I was at skate camp last summer, coaches would ask me to demonstrate my three turns and say "Those are good." So, how much of this was due to off-ice practice, I don't know. I do feel it made me more comfortable with the timing of the check, and my upper body position.
I've read of other people using a spinner for practicing 3 turns. It's probably harder to do them on a spinner, and if you have one it's worth a try. If I had access to one, I might give it a turn myself. Right now, I don't use the plate anymore as I'm happy with my 3 turns. The paper plate exercise, I feel, got me over the hump and cost me pennies.
N.B. If you have larger feet, you may need the paper platter. I have Tinkerbelle feet. I could do a 3 turn on a paper plate, easy peasy.