Setting an expectation for 100s in elementary school is reasonable, at least in my school district. High school is a little tougher, and I hope the classes will be hard enough to be a challenge, but if they end up relatively easy, I will probably set expectations high again. I think if you know your child's personality and capabilities, and you read over the homework being given at school, you should be able to decide where you want to set the bar. If my son is less academically inclined than my daughter, I will use a different method with him. Parenting is definitely not one size fits all.
Once in a while, my daughter will make a careless mistake, and I always just jokingly ask her, "What happened?!" She explains what she did wrong and how she will avoid making the same mistake the next time. Good enough for me. If there is anything she has a tougher time with, or if there is any topic she seems particularly interested in, we supplement at home and encourage extra study in that area.
I grew up with a tiger mom and my husband grew up with the total opposite, but we both ended up at the same Top 10 University, so I am trying to loosen up and go with the more pleasant method. All our siblings also were academically successful. Maybe it's just genetic and what I do doesn't matter at all. One can hope. In the end, I want my children to be self-motivated. I don't want to be their motivation. They need to be able to set their own standards and also learn to accept results. My role is to be supportive and always be available to help, but not to do it for them. I am focused more on teaching them proper habits, rather than giving them grief about any arbitrary grading. Grades are just one type of benchmark.