BBC Micro..
The Pi as a "BBC Micro for today" is one of those weird myths that is perpetuated despite all evidence to the contrary. The Pi was designed first and foremost as low cost accessible hardware, with the software environment left largely to the user and a challenge in most educational environments. In early days, you were on your own until ubiquity encouraged a slew of "get started with the Pi" kits that provided sd cards, cables, keyboards and cases to make sense of that bare board.
In contrast the BBC was expensive and prioritised quality and a complete environment over convenience. From the start it was possible (and encouraged) to put together a standard configuration that gave you an entirely predictable software and hardware environment on which you could learn. Equally, you might argue that the BBC was designed to make the hardware *more* accessible than the Pi - busses and interfaces proliferated, allowing the base hardware to be hacked, altered and upgraded. In contrast the Pi gives you a (very well) curated set of standard external interfaces around a tightly integrated and largely immutable core.
None of those differences are bad - they're a natural consequence of the evolution of the computing ecosystem - but they also reflect different goals for the projects. I'd argue the Pi is no more educational than any other SBC (and there are a lot), and the Pi Foundation have not done as much as they might have to address that use case. Indeed, it wasn't until the 400 that they addressed the challenges facing many classrooms of having a simple 'plug and go' option that helped with setup and cable management.
The PI is incredibly useful, and a huge achievement in establishing a ecosystem that many educators, developers and experimenters have grown to rely on, but it's achieved that through ubiquity rather than some sort of embodied 'educational design'. In that respect, the Arduino project is arguably better at presenting a user with a environment in which they can learn about both hardware and programming with a low cost device.