I will preface what I have to say by stating that I've never been a fan of physical punishment for children. I was never spanked as a child, my wife never was, and our daughters never were.

When I was studying developmental/child psychology back in college, on my way to becoming a teacher, we talked a lot about the different ways kids can react to something such as spanking. Every kid is different and some kids will be more willing to change from positive punishment than others. They are often the ones that are very close to their parents and looking to please them. That being said, they are also the least likely to misbehave. Others will respond badly to the punishment and drive them away from their parents, leading them to act against them more. A study I was reading just the other day talked about spanking leading to a large amount of anti-social and behavioral problems later in life. Here is a brief synopsis.

As a high school teacher I have seen this first hand. Using positive punishment with problem students usually drives a wedge between them and I, causing them to act out more and be less likely to respect me in the future. I often find that simply taking away their opportunities to act in a bad way is much more effective. Without a reaction, they are often left empty-handed and unsatisfied. When a student has recurring behavioral problems, we'll call in the parents. I have made a habit of asking them about their styles of discipline at home. A large number of the parents I have to speak to have mentioned that at one point or another they used physical punishment.

Now to address the issue from a philosophical point, I don't think that taking advantage of the human response to pain is necessary. It is a good thing when kids are learning early in their lives, knowing not to touch the hot stove or jump off the table, but when it is an external force, particularly one that is meant to nurture them, then it is not effective. Children need their parents to turn to as caretakers and role models. Having any association of pain with them will damage their relationships and mental growth. Additionally, the behaviors being modified likely are not harmful to the child's physical health. The instinct to survive does not come into play until they are being hurt, meaning they will just as likely "learn to survive" by avoiding their punisher than by avoiding the actions that led up to it.

I hope I at least somewhat addressed your question. I'm not too familiar with Heinlein unfortunately so I can't debate his arguments too much.