That is exactly the problem with kids today: too many distractions like their precious X-Box, MP3 players, etc. These gadgets are turning kids' minds to absolute and utter garbage. My parents were raised in the same era as this gentleman and they have taught me well. By the time I was fourteen, not only did I know my trigonometric ratios, but I was learning calculus and algebra as well as history and a few languages!
So to those whining about kids' distractions and how we should cut them some slack, you all need to grow up. Clearly this man wants his grandson to use the brain evolution has granted us to solve future problems and dilemmas, and not sit in front of the television like a mindless drone.
Children today are horrible at almost everything: reading, writing, and even speaking! We as a society, instead of hammering down and forcing these kids to learn, are accepting this blatant bastardization of everything we learned! Oxford professors are now accepting graduate dissertations with the phrases "lol" (and the like) along with horribly misspelled words that don't even phonetically make sense. It's absolutely disgusting that we, as a race of supposedly semi-intelligent beings, are allowing the works our ancestors studied for (and in some cases, died for) to be diminished and forgotten in lieu of the "short-hand" internet-speak. Disgusting. Einstein would be rolling over spitting in his grave, were he able to see the intelligence pool of the newest generation.
So, don't vilify or demonize this man for trying to teach his grandson some logic, reason, or some bloody math! I think this man should throw away the TV his grandson loves so much, destroy his skateboard and sit him in front of some books. First, the math (for the trigonometric ratios), and then some good old-fashioned philosophical treatises from the likes of Kant and Descartes.
To answer your question: it does not matter whether Einstein had problems in grade school, for that is not what we remember him for. Also, they're mostly stories told for inspirational value to the intellectually-subdued children of today's modern society. Unfortunately, we live in a time where it is permissible to be scientifically illiterate, yet everything requires a post-secondary degree of some form. This has to change. Just look at all these lay-people passing off half-formed and illogical opinions on matters they know nothing of. And it's these fools who have the ears of Parliament (or Congress). This has to change.
Those students from your past deserve your frustrated reprimanding condemnations. I applaud you for trying to get your grandson off the couch and to put his nose into some books. Quoting Einstein's apparent misfortunes in languages and manual dexterous abilities is not only irrelevant, but fallacious in nature.
I'm sorry I didn't entirely answer your question by providing you with sources, but I had to say my piece. Also, searching for these things is a colossal waste of your time. For, as I've mentioned previously, it is irrelevant to the current generation.