oooo long and very big subject ahead of you,
ok , where to start,
cockatiels basically mate...the first egg is prduced approximatly 10 days after the first
mating, the cockatiel will lay 1 egg every other day and can lay as many as 8 eggs, usual size of the clutch is 5 as a rule of thumb... the hen will start sitting the eggs after the 3rd egg is layed and will take approximatly 18 days for the first eggs to hatch from when they started sitting properly, , the rest will hatch at 2 day intervals,
stage 1 pic f a newly hatched cockatiel (this bird is just hatched and still wet , covered in yellow down that will later be replaced with pinfeathers..
http://i29.photobucket.com/albums/c3...ielhatch10.jpg
second stage is day 10 t 14 the bird will start to develop the pin feathers on the tips of the wings and the top of the nse where the crest will later be when fully feathered..
http://i29.photobucket.com/albums/c3...k/babytiel.png
third stage is where the wings are now vertually fully covered in pin feathers and small amunt of feathers that have broken free of the shaft .. the bird will have nw started to develop their pin feathers on the chest and tail feathers photo of the bird at around 3 to 4 weeks , the picture isnt a good ne but it shows the effect i want you to see...
http://i29.photobucket.com/albums/c3...ieljava009.jpg
the final stage is where the feathers on the birds middle back start to appear, they will then look vertually like a nrmal cockatiel exept smaller and spikey
http://i29.photobucket.com/albums/c3...ieljava008.jpg http://i29.photobucket.com/albums/c3...ckatiel010.jpg
the very last part of the bird to be fully feathered is the crop basically the top bit of the birds chest where the fod goes when the bird eats, as seen in the pictures below,
by this time at around 6 weeks the bird should have started to be weaned or fully weaned nto normal food with the exeption of maybe 1 or 2 feeds by hand a day, every bird is different in its weaning stage and i have had birds weaned completely from 6 weeks and sme not wean till 8 or 10 weeks... mst god breeders will judge when the bird is ready to try and let the bird go at its own pace and will not sell you a partially weaned bird for you to finish off, by now most of my birds have been started to wean or weaned completely but i usually wont let them go until i am satisfied they are eating and drinking properly, a lot of birds tend to lose weight over the weaning period so dont be put off if the bird is slightly on the thin side, it is usual in most cases.. by now my birds have already learned the step up command and if already payed for and name chose they will have learned to come to the call by name , .... sometimes at weaning stage the birds can get a bit nippy and frustrated, the trick with them is to be persistant and not let them get away with it, each breeder has their own methods of getting around this as , so do i,
http://i29.photobucket.com/albums/c3...redrump018.jpg http://i29.photobucket.com/albums/c3...nmickey007.jpg http://i29.photobucket.com/albums/c3...nmickey006.jpg
the finished result , fully feathered, fully weaned and ready to go, comes to the call and sits and plays nicely with the new owners, silly tame, as tame as they can get mine include in most birds lying on their back wanting a tickle
http://i29.photobucket.com/albums/c3...abytiel001.jpg
i hope these picture guides help you, while the dates are not completely accurate as the titles are from folder name, nt actual name of photo, but the dates i have stated to you on this are accurate to the birds pictured...
i wish you good luck with your new bird and if you have any problems or want advice n it please let me know and i will do my best to help you,
i would also ask all people n this thread to respect my copyright of the pictures and not to reproduce them in any way!!
i did post direct images but appears images are disabled on here , guess it saves the bandwidths, so click n the links and have a look

hope it helps !!
katie