No ethical values? Hah. Not only do schools have such things as Character Counts but, hey, literature and history will involve ethical values in the discussion of characters and events.
Now, it is quite so that little grade schoolers will not be able to understand the practical moral philosophy concept of why XYZ behavior is “wrong”… but the thing is, whatever the foundation of the ethics… well, there’s no PC way of saying it… even then * while they are children, we don’t owe them explanation to their full satisfaction before they deign to behave properly.* As their minds develop we must then introduce them to the deeper explanation of actions and consequences, things that are hurtful to others and to society, and of fairness and playing by the rules, and of respect for others’ welfare. Not stealing, not assaulting, not cheating, not lying maliciously, not being a leech – that can all be a part of Societal Ethics, the morality of ordered, organized, by-certain-general-rules play for the sake of a better quality of life for the entire tribe than if everyone is just following their impulses helter-skelter and hitting each other on the head with sticks.
For instance, the older version of the Golden Rule – Do NOT do to others what you wouldn’t like done to you – is a strong ethical statement AND need not be referential to any “higher authority”, yet it can be taught at an elementary level. (“That hurt him. How would you like it if someone hurt you?”)
Now, if the educational system and/or the teachers are unprepared for this and allow the kids to totally flummox the teacher by merely asking “why?”, well, sure the kids will conclude we’re making it up just to be contrary. That’s another story.
In the absence of mature reasoning, we pretty much have to start by conditioning children on that some things Are Not To Be Done, THEN we slowly explain the cost-benefit analysis, simply at first and later in a more sophisticated manner. Basing the “values” on a religious foundation could be seen as the ultimate “because Authority said so, so shut up” scenario --because you would never have to justify the rules even to adults! (BTW, At least from my POV, when I was 6 “because teacher says so” and “because mom says so” would have carried far more weight than “because Jesus said so”. Mom and the teacher, after all, were THERE.)