gallito89, those individuals at the school district didn't know what they were talking about and the Internal Revenue Service has an entirely different viewpoint on it and their viewpoint is the one that counts.
Let us assume for a moment that you made $500 from each of 20 different sources during the year. You didn't make $600 for any of them, but you made a total of $10,000 for the year. Those school district employees or employee is saying that the Internal Revenue Service doesn't care about that $10,000 you made because none of the sources paid you more than $600 during the year.
What if there were even more sources. None of them paid you more than $600 a year, but the total was $20,000? What if it was $50,000. How about $100,000? What about one million dollars?
That school district employee or those school district employees should be taking some classes about taxes since the information given is absolutely wrong.
As Linda and Kevin said, the Internal Revenue Service wants to know about all of it.
You can find a lot of useful and reliable information at the Internal Revenue Service site. Here is a link to their site
Internal Revenue Service