Far from it. The reality is that students performing at the top of the class in 4th grade tend to be the same students performing at the top of the class in 12th grade, due to many factors that tend to remain stable in students' lives: family, lifestyle, resources, etc.
Being branded with a low IQ at a young age, in other words, is like being born poor. Due to family circumstances and the mechanisms of society, most people born poor will remain poor throughout their lives. But that doesn't mean anyone is innately poor or destined to be poor; there is always potential for any poor person to become rich.