I love duct tape. First, it is good for talking back. Second, you can make it so they can't get out of the chair or hit you. In some cases, you can simply duct tape the pencil to their mouth and let 'em do it the hard way. JUST KIDDING. Lauging Aside.
My grandmother taught first grade her entire life. On the side, she would tutor the children that were doing poorly in school. Parents would come to here very frustrated and she would get them to do well again in school. What was her talent? She was good at discipline. Many of these kids just needed to know that opting out wasn't a possibility. She was very succesful at helping a lot of kids.
My parents didn't teach me the alphabet or anything about numbers. So, about first grade, with almost 0 knowledge, I went to my Grandmas for the summer and learned the entire first grade, was able to read, and then some. All it boiled down to was we worked diligently every day. I cried every day for the first month. I had never been made to work hard or sit still. It seemed so difficult. But , soon I learned I could do it and started to enjoy it; especially after I started doing well. It helped my entire life in school because I had learned what was expected and the work effort required. Some of my brothers didn't get this and struggled all the way through school.
So, in my mind, the kindest thing to do is to teach your child how to work hard, focus, and overcome problems. Once they get this down, they develop self-esteem and learn to love school. Sure, it's hard at first as all children cry and scream to get their way, but real discipline only takes a month or two to get down and it gets quite fun after that.
There is a pre-school here that has most of the students reading and doing math before before kindergarten. It's one person with one assistant. How do they do it? Instead of playing the entire time, they work for a few hours a day. The teacher expects the children to stay on task.
It's great to have fun in life and be carefree, but it's more fun to do things that are interesting and challenging. A child that learns discpline and hard work will be able to have more opportunities for such things.
If you think this is strict, go read about the Tiger mothers (Asian Parenting). Working a couple hours a day is actually pretty mild. Asians, by the way, are much more likely to succeed in our America culture (statistically).