Teachworks allows you to send an email to customers when a payment has been received or recorded for their account. Payment notifications are set in your companies Account Settings:
Go to the Account & Settings tab and click on Account Settings
Scroll down to the Invoice Settings section and set the Payment Received Email to "Enabled".
Save the form.
When enabled, the payment form at the bottom of your invoices will display a checkbox to send a Payment Received email. If you accept payments online and a customer makes a payment the payment received email will be sent after the successful payment.
You can customize the Payment Received template by following the instructions here: Customizing Notification Templates.