Starting from the very basics, we must realise what the differences between a Dinghy & a Keelboat are, i.e. what makes a keelboat a keelboat and why does sailing one require us to have additional knowledge to that of a dinghy instructor...
The most obvious extra considerations are as follows:-
Launching & recovery -
Possible engine use - Inform your crew on use, make sure there is a safe place to store when under sail, consider the engine in your pre-launch/departure checks. You will also need to consider additional items such as safety, starting, running procedures, fuel storage, stopping, handling under power - particularly when an engine is used to recover a man overboard, come alongside or when mooring.
Risk of swamping - Please realise that this is a possibility! Therefore a need for safety cover, contact with a land/water support unit and a means of attracting attention are required.
Method of tack & gybe - Treat it as though it is an aft-main boat i.e. step over the tiller/ lift the tiller
Gybing - Bring mainsail into centre before gybe to reduce weight movement, only swop sides once gybe is complete.
Crew & helm 'jobs' - i.e. Helm controls tiller, whilst crew controls main sheet
Man Overboard recovery - Preparation for this eventuality will need to be done prior to departure; by briefing your crew/students about the various methods of recovering an MOB, i.e. with a ladder, mainsheet, parbuckling with the jib or using a 'handy-billy' from the boom.
Possibility of grounding - Leeshore dangers, wind & tide have greater effect.
Boat weight - The difference in methods of completing some of the slow manouevres is quite difference, you firstly carry more leeway, in addition to this you may have picked up the habit of 'fending off' with a part of your body in your dinghy/catamaran - you certainly don't want to be doing this in a keelboat!
Companion way/cabin - It is sometimes recommended that you remove the need for your student to enter the cabin other than when the boat is at rest. By doing this you can make sure the cabin is kept tidy and avoid any accidents 'down below' and out of your immediate sight. Remember to keep the companion way closed at all times when noone is below to reduce the risk of someone falling down it! You must remember to brief your students/crew about the trip hazard of the companion way roof.
Clutches/Spin Locks - Explain the advantages, disadvantages and issues.
Winches - Risks of trapping fingers, awareness of uses i.e. how and when
Mainsheet traveller - If you have sailed Catamarans before then you may well be familiar with a mainsheet traveller. An explaination of the uses including when, why and how is imperitive.
Jib car & track - Designed to de/increase leach/foot tension. An ideal setting for example is running on a 45 degree angle.
Back stay - Effects of increased & decreased rake i.e. increased = tip of the mast will be moved aft - you can show this with a ruler - i.e. the centre of effort of the boat is moving aft.
Boom - Now this may be an obvious one, but if you have come from a dinghy sailing background then you have probably been clipped around the head on more than one occasion by the boom; unfortunately this can be far more terminal on a keelboat!
Keel (i.e. only '4 essentials unlike a dinghy with '5') - there is a far greater difference in the clearance/depth required. There may be a lifting keel which could reduce this problem but again the dangers of a lifting keel must be realised, therefore good tuition & guidance on the uses along with a 'lock-down' device are important.
Use of instruments (i.e. depth sounder, GPS etc)