Verbs may change their spelling according to which tense is being used.
The resources above cover the following skills:
Conventions of Standard English
Demonstrate command of the conventions of Standard English grammar and usage when writing or speaking. [L.3.1]
Form and use regular and irregular plural nouns. [L.3.1b]
Form and use the simple (e.g., I walked; I walk; I will walk) verb tenses. [L.3.1e]