This applies not only to marriage, where it is obvious that the child will get a message from both parents;
but also to teachers who are hired to teach the child,
to authors who are paid to write the books for your child
to the administration who does whatever they do in the school system
and to the corporations who make the profit off of writing
and selling the books for your child,
and to the government who takes your tax money to pay for half the book price;
so they can direct the writing through the department of federal education
and to the university departments which do so-called research in how to educate a child;
and to the U.N. which guides and influences the universities through grants and fundings.
And since money flows through it all, from the U.N. down,
or from your pocket up to the U.N. through Congress, and then back to the universities that set up text book plans:
why should you trust the plan laid out to teach your child without a close inspection?

Because what you do, proceeds forth from what you believe in your heart, the seat of your desire, the thing that pumps life into you to do what you will, that which moves you.
It's the same with everyone. Be not unequally yoked. Not in marriage, for your spouse will train your child differently from you till your child rejects you and all you believe; neither in the hiring of school teachers, for the teacher will teach according to his beliefs, nor in the writers of books that you buy; for they will slant even your own ideas to a stage that paves the way for their ideas.

Training up children is not to be left in the control of those who differ from you.

When it comes to planting seeds in the mind, watch carefully. The word of God is likened to a good seed.
The word of John Dewey is another seed entirely.
John Dewey is the father of modern education.
Even the word education should be studied to learn its historical roots.

Who writes the books?
What is their goal?
What do they believe?
What do they want for your children?

Even the Christian teachers in Germany during the 1920's and 30's conformed to the system for fear of their paycheck.
Is the Bible the only true foundation for knowledge?
Training up children should not be left in the hands of someone who does not hold our values.
Why do you think men and women are commanded to not take a spouse outside of their faith? The answer is partly because of the training of the children, and partly due to the influence on the husband.