What day do you consider to be the first day of the week? To me, it’s always seemed natural that it’s Monday (because that was the first day of the school week, I suppose), but for some people, it’s Sunday. This seems odd to me, given that Sunday is part of the weekend (note the word end in there). And there’s also the fact that the Bible talks about God resting on the seventh day. But of course this only works if Monday is the first day; for those of Jewish faith, the rest day, or Sabbath, is Saturday.
Of course, most of the time none of this really matters – we just get on with what we have to do on Monday, Tuesday and so on. Confusion arises, though, if, during a chat on Friday, someone starts talking about their plans for ‘next week’ and then refers to ‘Sunday’; I’m thinking about over a week away, but they might mean in two days’ time. And if we’re supposed to be meeting up, that could be disastrous. So, to be on the safe side, remind your students to always specify the date as well as the day!

As far as I know, “Sabbath” is the equivalent of “Sunday”, therefore the first day of the week is Monday.
According to: http://en.wikipedia.org/wiki/Saturday Saturday is the 7th day for many people.
You mention the sabbath in the Bible, (Saturday, Sábado, in Spanish and Portuguese, Samedi in French come from that, I think). For the Hebrew people of the Bible, celebrating the sabbath would indeed be on our Saturday – that’s the day God ‘rested’. The day after the sabbath was the day of the resurrection and was ‘the first day of the week’ (see in the bible, Luke 24 “On the first day of the week…. he has risen!”). This was our Sunday, which only became the ‘rest’ day when Christians started to celebrate the day of Christ’s resurrection. Therefore, following this logic, Sunday is the first day of the week!
Of course, Monday is the first day of our working week or school week! (ie Mon-Fri!)
The Bible also calls Sunday the first day of the week when speaking about the day when Jesus rose from the dead. Matthew 28:1reads, “After the Sabbath, at dawn on the first day of the week, Mary Magdalene and the other Mary went to look at the tomb”.And goes on to tell the story of Jesus’s resurection. So it is the first day of the week not only people of Jewish faith, but also for Christians.
It refers a Bible reader to the first day of creation.The day when Jesus reaises from the dead becomes day one of the new creation. The new creation in Jesus Christ, the day when death no longer has the final word. Which is also why Sunday is the sacred day for Christians.
Some calendars reflect this by having Sunday at the beginning of the week, not at the end.