Very basic Linux for educational purposes

There isn't such thing as "standard Linux". For learning (what do you want to learn, specifically?), a minimal install of Slackware should do.

You can easily build a kernel that boots, but it will be useless without userspace applications (e.g. shell and utilities).

If you want to build your own system from scratch, check Linux from Scratch.

Linux From Scratch (LFS) is a project that provides you with step-by-step instructions for building your own customized Linux system entirely from source.

Slackware should do.

And to be honest - there is no "standard" linux.

You define your standard afer you defined what you need to do with it and what to expect from it.

The low-level (plug and play, device-naming, network configuration, system configuration, detection of network services, hardening) is quite different on different linux distributions. Even init-scripts and how they get processed during boot is different.

You might try looking at a BSD distribution. If you are mainly interested in having a look at how Unix works than the BSDs are nice and clean in my opinion, especially the so called base system, which you sound like you are interested in is clearly separated from the applications etc. I recommend FreeBSD, because, once you've had a look around, you may decide to stay, and FreeBSD has an extensive port system, which gives you the chance to build a the custom system, you want.

Another perspective is to play around with Linux From Scratch (LFS)-- although, in my experience, this is a larger commitment.