Question: We realize that knowing the vocabulary is important in every subject. What we don't know is exactly what words our children in grades 3, 7 and 9 should know or how to help them learn unfamiliar words. -- More Vocabulary Wanted
Answer: The simplest answer to your question is that your children should first of all know the words used in their textbooks. In the very early grades, these words are generally those that are found in their readers and will usually be formally introduced by their teachers. Later on, when your children are reading content area materials, the important new words in each chapter are generally shown on the first page of each chapter and frequently discussed in class.
Of course, students need more than a textbook vocabulary. Over the years, studies have been done to find out the specific words children should know at different grade levels. On our website (dearteacher.com), you will find well-researched lists under "Skill Builders" -- "Reading."
To know what words children should know is handy; however, it is essential that they also know what most of them mean. The best way for them to acquire these words is through extensive reading -- not an isolated study of words. Parents can help their children by defining unfamiliar words heard in conversations and appearing in stories with kid-friendly definitions.
If older children can't understand new words from the context, they should get in the dictionary habit, which is easy to do with electronic readers. You just tap a word to get its definition.