Identify the adjectival clause in the sentence below.

The school where my cousin attends is too blocks away.

The adjectival clause is: "where my cousin attends". Adjectival clause which is also known as the relative clause is a clause (group of words with both the subject and the verb) that act as an adjective and cannot stand on its own. Here the clause is introduced by a relative adverb "where" instead of a relative pronoun which is usually what introduces a relative clause.