Last week I took a lesson on http://www.convoconnect.com. It is a website which connect you with teachers from around the world who offer all kinds of lesson offerings for you to chose from all at different prices. You can check out different teacher profiles, see their experience and qualifications, and view their electronic calendars in real-time to see what availability they have. Once you have chosen a teacher you just top up your account and use credits to purchase the lesson. the lessons then take place online, on Skype.
