Advice to a new-comer

Dar is a peaceful place in general. People here are warm, friendly and helpful. One of the downsides is that it's the 12th dirtiest city in the world - so you have to get used to the sight of crows eating litter, drains full of rubbish and sludge, and filthy wastewater flowing onto the streets. The drainage and sewage system are not up to standard and all the city's sewage gets dumped into the ocean; this is the source of the unpleasant smell you'd experience as you drive along ocean road. Tz still has a long way to go before it becomes as developed as SA.
As for security, it all depends on where you live; if you stay in places like Gongolamboto and Manzese for example, chances of being robbed will be higher than if you were to stay at a fully secured apartment at Mikocheni or Msasani. Yes, you can move around freely - just make sure your handbag isn't hanging loosely over your shoulder.  There are some cases where people's bags have been snatched away by bikers – this had also happened to my colleague's friend. Getting around isn't difficult; you can opt for public transport, taxis, bajajs or motorcycle taxis aka boda-boda. If you lose your way, there may be a good samaritan around to give you directions - without expecting cash or anything in return.
I strongly advise you to learn basic Kiswahili so that you'd be in a better position to negotiate and bargain, plus avoid getting ripped off.
My brother studied in IST for about 2 years but my parents transferred him to another school because their standard of education wasn't  good compared to the British curriculum. They seemed to focus more on fun, games and activities such as horse-back riding than studies; perhaps you should consider other schools like Laureate International School or St Mary's International School.
I really miss fireworks!  These are prohibited by the government, and well, the outcome is that festive seasons here go by so quietly without a display of lovely colors in the night sky!
There are many interesting places to visit and I recommend you start with the National Museum.
Enjoy your stay!

Welcome to Dar es Salaam Beata. As mentioned by Seribn earlier that's how Dar is. I just want to advice on educational institutions. IST is probably the best school, but it depends on your tastes. I would recommend Dar es Salaam International Academy (DIA) It offers IB curriculum, but is small yet very organised.

You can also try to get an apartment in Upanga or the in the city centre though they are expensive.

I hope this will help.