Retired Teacher does have a good idea.
I'm not a teacher myself, but I was asked to create a
bubbletest sheet for a teacher and it evolved into a rather
big project: http://www.catpin.com/bubbletest
I now am making money from the Google-Ads and wonderful
donations from teachers. I don't make a living at it, but
it helps pay for my webhosting each year.
As a teacher, you might have a good idea, or something that
teachers really need that isn't already offered. I was
amazed that nobody had a bubbletest generator yet ... it was
a surprise to me. The site now gets over 250 visitors each
day (during the school year).
If you have a great idea and want to know how feasible it
is to develop online, contact me using my website ...
see link below.
I certainly think you should learn HTML and CSS, but teachers
have good insights into what other teachers need.