A number of our coaches are using electronic invoices: they e-mail out a PDF file with the invoice amounts, said invoice being generated from their accounting software; or for the less tech-y, an e-mail listing the lessons in the body of the message.
We also pay them electronically ... which is handy. One coach uses a pocket voice recorder to keep track of lessons and lesson length instead of writing them on paper.
Perhaps it's like my rink: the coaches don't collect the money directly; the rink or Club accepts the electronic payment and disburses it to the coach later. I get a check every two weeks from the rink for the group and private lessons (less commission) I've given over that period.
The fly in the ointment is that the private-lesson amount is a single number, so if it doesn't jive with my records, I have to figure out why the balance is off. Sometimes if I run over on lesson time, a family might pay for 15 minutes of extra time without giving me a receipt, which is generous and unexpected. Sometimes, when it's crowded and noisy at the desk, the clerk accidentally logs a 30-minute as a lesson for another coach. (Her name sounds similar.) When the latter happens, I don't get paid: my revenue goes to the other coach. That takes weeks to find and correct in the system. It's really fun when both things happen: it looks like I was overpaid by 15 minutes when in reality, I lost a half-hour lesson.
The Rink's system is flawed: they don't know how to get a list of all lessons for a particular coach out of the application. I end up taking my list of receipts to the rink to go through them with the desk clerk, looking things up. Think of balancing your checkbook when all you have from the bank is the current balance.
I used to use a paper week-at-a-glance calendar, which was overkill and bulky. Then I tried using my phone's calendar, which is okay, but tedious to log completed receipts. Now, I use a combination of my phone calendar (for reminders) and a paper worksheet each month. Mid-week, I write my scheduled lessons with an "S." I overwrite the "S" with the lesson lengths and circle the ones for which I have receipts.
Most of the online calendars let you set up recurring appointments with reminders via email or SMS.
Yahoo! lets you send an invitation for an appointment in advance with a yes/no choice for the recipient.
I've used that on occasion when a skater's just started and is having trouble remembering to show up, lol.