There's a lot to say about the relationship to Torah that a grandfather has to his grandchild...
A grandfather is obligated to play a role in educating his grandson in Torah study. The Gemara in Kiddushin 30a relates how the grandfather of Zevulun ben Dan took pains to teach him halacha, gemara, mishnah, chumash and aggada. Such action is no small feat, and clearly underlines the importance attributed to a grandfather’s position in chinuch. Whilst learning in such depth with one’s grandson is perhaps harder to accomplish these days, every grandfather must endeavour to maintain an avid interest in their grandson’s talmud torah. This obligation is famously derived from the words:
"והודעתםלבניךולבניבניך"
“You shall make them known to your sons and your grandsons” - Devarim 4:9.
Indeed, such is this commitment to teaching Torah to one’s grandson, that chazal view it upon doing so, as if he had personally received the Torah from Har Sinai.1
This idea is illustrated beautifully by the following story related in the Yerushalmi Shabbos 1:2. Rabbi Yehoshua ben Levi had the practise to review everything that his grandson had learnt with him every erev Shabbos. One week he forgot his usual undertaking, and instead made his way to the bathhouse in preparation for the coming Shabbos. Upon his arrival he realised his mistake, and instead of washing, quickly clothed himself and returned to learn with his grandson. His student Rav Chiya, witnessed the turn of events and questioned his Rebbi’s actions. Previously they had learnt that if a person were to go to the bathhouse and undress, and then remembers that they have not yet davened, one does not need to don his clothes again. Rather one may bathe first and can then go to daven. If this is so, why did Rabbi Yehoshua ben Levi feel the need to swiftly return to his grandson without having first bathed himself? Rabbi Yehoshua ben Levi duly responded that listening to the words of Torah from his grandson is like hearing it directly from Har Sinai.
Rabbi Boruch Ber Lebowitz זצ"ל sums up in a most clear-cut and succinct fashion. He notes authoritatively:
"שהחיובהואעלכלאישואישמישראללראותשבנוובןבנויהיולתלמידיחכמיםוגאוניםבתורהשנאמרושננתםלבניך"
“There is an obligation on each and every Jew to see that his son and his grandson become great Torah scholars as it says ‘And you shall teach it to your children’”.2
One cannot maintain a nonchalant approach to their children and grandchildren’s spiritual development. It is a task that lies with both a father and grandfather to ensure that their progeny are receiving a suitable and effective Torah education. Through the correct schooling and choice of yeshiva, a child will begin to start realising their potential. This overarching obligation must remain at the forefront of one’s priority, and must not be compromised. In fact, such is this responsibility, that some poskim mention that even the grandfather must help to fund a child’s tuition fees.3
1Kiddushin 30a writes, "אמררבייהושעבןלויכלהמלמדאתבןבנותורהמעלהעליוהכתובכאילוקבלהמהרסיני" –“R’ Yehoshu ben Levi said: Anyone who teaches his grandson Torah it is as if he had personally received [the Torah] from Mount Sinai”. The גמרא goes on to relate two stories of Amoraim who embodied this commitment to furthering the Torah knowledge of their grandsons.
2 See תשובהלרבאחדבאשכנזבדיןמצוותלימודהתורה–ברכתשמואל, קידושין, סימןכז
3Shach, YD 245:1. Also note Shu"t Rabbi Akiva Eiger, Siman 42 - 'ברכתלהכניסוביתום'. R’ Akiva Eiger notes down in the name of the Kessef Mishnah the following:
"ועייןבכ"מהל'ת"ת (פ"א, ה"ב) דמחויבאפילולשכורמלמדללמודעםבן, וא"כלהכניסושייךיותרעלאביהאב"
“And over there in the Kesef Mishna Hilchos Talmud Torah (1:2) [it states] that one is obligated even to hire a teacher to learn with the son, and if so, how much more so is it fitting that the grandfather enter into this obligation”.