Will the children partake in the planting/tending of the raised bed? Are you/they planting vegetables? Is it part of an educational program?

Nandina is one of the most reliable shrubs, is evergreen and has interest all year. Or one of the Sambucus.

Hi, welcome to GoY, it sounds to me that your first job is to take out the soil from the raised bed, and get rid of the tarmac, otherwise it will eventually just fill up with water, half a meter isn't very deep, especially for a tall shrub.
If you just have a look online for thornless tall shrubs you should get quite a large choice, but a lot depends what you consider to be a tall shrub, many ''shrubs'' can grow to almost tree like proportions, so it depends on what you want the ultimate height to be, Derek.

Sorry to be a killjoy but seeing that the bed is on top of tarmac and only 19 inches deep, then I would not look to plant anything that is too big as it will dry out very quickly in the summer. Also consider the school holidays when there won't be anyone to water it.

My thoughts too. It isn't deep enough for most shrubs and there could be problems either with drying out or lack of drainage, depending on the weather. If you can't remove all the tarmac could you at least get some largish holes drilled right through the substrate? Otherwise you will just have to treat it like a large pot.

Another thought - if those things are impossible at this stage how about drilling a few holes at the base of the retaining wall to avoid any waterlogging, and putting something water retaining such as gel crystals on the base to help in dry periods.

How big is the bed?

There are two raised beds at my local junior school of the height you've mentioned. They are situated in a public area between the school wall and the path.

Last summer one was planted with herbs...Rosmary, fennel, sages, thyme, coriander and parsley.. These were growing for anyone to take snippets and for the school to use in their cooking. The other....cherry tomatoes, edible flowers such as nasturtiums, violas, marigolds.

I take my dog walking that way and the beds were such a treat to see, not vandalised at all and opposite sheltered housing where they provided a pretty view and also edible treats that many people weren't able to grow themselves.
I'm looking forward to seeing how they are planted this year...they'll have a hard act to follow..

Welcome to GOY Pamelaclare. Can you say how long and wide this bed is? Why do they want height at the back of the bed if it is accessible from all sides? Depending on the length of the bed, the height might be more appropriately placed in the centre of the bed equidistant from the three sides. at one end. Is the bed intended to be an all year long feature or just a summer project. What is the distance between the back of the bed and the nearest boundary? Is this going to be a wild life attraction? Small buddleia are available which would attract butterflies etc. Hebe comes in lots of colours and holly or cotoneaster would give you flowers and berries. Shrubs of the size required to give you the height you desire will also grow out the way. Once you establish a shrub you need to ensure you will not disturb all the surrounding plants should you wish to replace it. Planting it in a pot with the bottom cut off would allow you to grow something like a eucalyptus tree. My daughter had one in a pot in a semi shady area for several years and it was very happy. A light trim to use the foliage with cut flowers was more than adequate. I have a Kojo-no-mai in a raised bed and it is growing well.