The teachers who took part in the program also told me of their worries that they might be force-feeding their pupils information rather than stimulating the discussion necessary to ensure they grasped the importance to them of what they were being taught.
主语The teachers 后跟who引导的定语从句。also told me of their worries是谓语部分，their worries后跟that引导的同位语从句that they might be force-feeding their pupils information rather than stimulating the discussion说明worries的具体内容。necessary to ensure是形容词结构修饰discussion。ensure后面的宾语是一个省略了引导词that的宾语从句they grasped the importance of what they were being taught。to them是插入语，“对他们”。
tell sb. of sth.告知某人某事
force-feed强行灌输(force-feed sb. sth.)
grasp the importance of…掌握…的要领，关键内容