Calculators and velcro.
My kids were never allowed calculators during their homeschool career.
I never allowed footwear that didn't tie.
Between calculators, velcro and TV, I'd guess at least 50% of basic skills are not lost, but never learned, to the detriment of a child's (and ultimately adult's) ability to formulate thought processes (sp?) required to reach a conclusion quickly and easily.
Footwear that doesn’t tie is a great invention!!!!!!!!!
My daughter is special needs. She can do lots of things (ride a bike, swim, great at math). However, she cannot tie her shoes tight. She finally was able to tie them when she was about 9 or 10, but they still always come untied. A couple of the kids that have similar problems are in high school, and they still can’t tie their shoes tight.
Anyway, we are very thankful for shoes that don’t need to be tied.
I would die without velcro. I hate tying shoelaces. My 10 year old daughter is better at tying laces than I am, I hate it that much.
As for calculators, we rarely use them around here. My daughter helps me with my books, she's pretty much in charge of inventory control and never uses a calculator, and rarely, if ever, makes a mistake.