In the first parsha of Shma we say ושננתם לבניך and Chazal say that בניך refers to תלמידיך.
In the second parsha we say ולמדתם אותם את בניכם - where the word בנים means sons and we don't expound it to refer to students.
What is the difference?
One can be a son even if the father teaches him nonsense. But one can only be a תלמיד if the Rebbe teaches him Torah. There is no other way.
In the first parsha we say "השם אחד" and allude to the end of days where all that exists his the will of Hashem. There are no other options. In that parsha we say that בניך refer to תלמידיך b/c in the context of the end of days, the only option is Torah. There is no other way to be a תלמיד other than by learning Torah. At the end of days there is no "other side". In the second parsha בניך refers to sons כפשוטו b/c there is also an option for one to be a son w/o the father teaching Torah. In the second parsha there are other options. There IS a "צד שכנגד".
ודוק!!!
[עפ"י דברי מרן ראש הישיבה זצ"ל]
