I first encountered a chatterbot, it was ELIZA on the Tandy/Radio Shack computers that were in the first computer lab in the junior high school where I taught in the 1970s.
ELIZA is an early natural language processing program that came into being in the mid-1960s at the MIT Artificial Intelligence Laboratory. The original was by Joseph Weizenbaum, but there are many variations on it.
This was very early artificial intelligence. ELIZA is still out there, but I have seen a little spike in interest because she was featured in an episode of the TV show Young Sheldon. The episode, "A Computer, a Plastic Pony, and a Case of Beer," may still be available at www.cbs.com. Sheldon and his family become quite enamored by ELIZA, though the precocious Sheldon quickly realizes it is a very limited program.
ELIZA was created to demonstrate how superficial human to computer communications was at that time, but that didn't mean that when it was put on personal computers, humans didn't find it engaging. Sure, kids had fun trying to trick it or cursing at it, but after awhile you gave up when it started repeating responses.
The program in all the various forms I have seen it still uses pattern matching and substitution methodology. She (as people often personified ELIZA), gives canned responses based on a keyword you input. If you say "Hello," she has a ready response. If you say "friend," she has several ways to respond depending on what other words you used. Early users felt they were talking to "someone" who understood their input.
ELIZA was one of the first chatterbots (later clipped to chatbot) and a sample for the Turing Test. That test of a machine's ability to exhibit intelligent behavior equivalent to, or indistinguishable from, that of a human, is not one ELIZA can pass by today's standards. ELIZA fails very quickly if you ask her a few complex questions.
One variation was called DOCTOR and was made to be a crude Rogerian psychotherapist who likes to "reflect" on your questions by turning the questions back at the patient. This was the version that my students when I taught middle school found fascinating and my little programming club decided to hack the code and make their own versions.
Are chatbots useful to educators? They have their uses, though I don't find most of those applications to be things that will change education in ways I want to see it change. I would like to see them used for things like e-learning support and language learning,
If you want to look back at an early effort, you can try a somewhat updated version of ELIZA that I used in class at my NJIT website. See what ELIZA's advice for you turns out to be.