Luckily Austria is a beautiful, friendly country and the school children are for the most part a pleasure to teach, because volunteering with the Austrian Bilingual Classrooms Initiative is not something I would recommend.
For a start, the program revolves around games ('Active learning', which means children running around) and songs. Expect to do a lot of this, and very little real English teaching. There are a few games which have useful grammar and language content, but they are minimal. If you do not enjoy being in the role of cheerleader, this program is unlikely to provide you with much teaching satisfaction. It will also pay to dispel any ideas of Not-for-Profit goodness early on, as this program charges the children a fee for participation, while being well funded from other sources besides.
Secondly, constructive criticism is not welcome, nor are complaints. The managers are either rude or temperamental (the director, did not introduce himself and I did not meet him until I accidentally bumped into him a week and a half into the program). We were provided with very limited food supplies for the first week, and when I complained about this I was told that I raised the matter at an inappropriate time, that disciplinary action was needed; that all ABCI's crushing force would be applied to such dissidence in the ranks.
Expect to be working flat out and FULL time. Getting up at 5 o'clock in the morning is not unusual (despite what they will tell you). The schools are usually a long commute from wherever you are staying, and even in Vienna it is often necessary to take public transport for an hour+ to reach schools on time. When you get back late in the afternoon, there is usually something to prevent you from relaxing too much (meetings, the Virtual Classroom, or practicing new classroom content in front of colleagues when they decide you need to learn a whole new program). In short, all of this means that this program is more stressful than any paid position I've been in-- there is no time or place to talk to anyone or discuss grievances, and you end up feeling exhausted and unmotivated.
They will tell you that all of the above is to be expected, because it is a training program for which a qualification is awarded. Don't be fooled by this-- you will get a piece of paper which is worth very little in real terms. Unless you happen to be an 18 year old school leaver with no qualifications, it is unlikely to be of much use to anyone.
Also, don't expect anything to happen efficiently unless it is of benefit or consequence to the organization. As a trainee you are expected to be punctual and well organized (fair enough), but they will not return this favor where it is your time or resources at stake. Expect long waits for people to turn up, don't expect prompt reimbursement of your monies (my flight reimbursement arrived 2 months after I left; the certificate took even longer). Disorganization is the norm, so from time to time you may have no internet access, or no washing machine for a couple of weeks. Similarly, safety of participants is taken rather lightly-- there was a seat belt missing in a vehicle, which I mentioned early on. Nothing was done about it, despite high-speed travel on the auto bahn being a regular phenomenon.
The academic side of the program is equally sloppy. You will be asked to create new content (preferably original) for which no reference is included in any of the program booklets. As anyone with any academic background will know, this effectively constitutes plagiarism.
And finally, the staff predominantly consists of young males, particularly amongst the teachers. Some may not mind, but I believe it does influence the outlook and attitude of the organization to some extent. On the plus side, the senior teachers are for the most part a great bunch-- it is the managers that bring it down.
If you are young, unqualified and willing to tolerate all of the above, this may be the place to develop your cheerleader skills. If you are not, then I'd recommend trying another program.