The study found that the kids when they were five, six or seven, who had been watching more violent TV shows had grown up to be more aggressive adolescents as compared to the adolescensts who had been just as aggressive in childhood but had not watched as much media violence.

首先这个句子有一处语法错误：the kids后的定语从句为限制性的，关系代词应该尽量接近先行词，而不应将定语从句的时间状语从句提前到先行词与关系代词之间。正确的定语从句结构应该如下：

The study found that the kids who had been watching more violent TV shows when they were five, six or seven had grown up to be more aggressive adolescents as compared to the adolescensts who had been just as aggressive in childhood but had not watched as much media violence.

compared to为过去分词短语，可以作状语或定语。有时可以在过去分词前加as, 构成as+过去分词短语结构，意义不变。例如：Let's have a look at the numbers (as) shown in the chart. (让我们看一下表格中显示的这些数据。）通常不需分析as是什么词类。本句中as compared to 为状语，表示比较级的比较对象，可以改为compared to 或者 than。

第二和第三个as均为副词，分别修饰aggressive和much, 意为同样的，省略了as比较分句，因为比较对象就是前面的the kids who...。类似的句子为：

Tom is 1.9 metres and weighs 200 pounds. Jonh is as tall, but not as heavy. (比较分句as Tom没有必要说出）