Is this an overt or covert study? Participants' anonymity must be maintained. If possible, informed consent must be obtained. These are the two most important ethical considerations. Including your own reflections is ok, provided it is made clear that this is what they are and are included in the section on discussion. The study should be about the evidence gathered, and reflections should not play a part in this.
I agree with the ethical concerns raised but I'd also ask why introduce yourself into the study? Are you there to influence the discussion/observations or to learn from them? Sometimes your presence is an influence whether you intend it to be or not, but purposely deciding you will be of influence is different and deserves a rationale consistent with the research.
Your case is a peculiar one. May I ask which method are you applying to this research and more so how will you be able to be objective here? ethical consideration stands notwithstanding your involvement.
In response to Philip Mccallion, it all depends on the issues I raised, that is, is this a covert participation or overt participation study? If it is covert then the presence of the researcher should not influence outcome. If the others are aware of what is going on then this could cause the Hawthorne Effect to arise. The researcher has not responded to clarify this issue.
Researchers journaling during the intervention may be an acceptable qualitative data source, but simply interviewing yourself as if you were a regular participant would probably not be appropriate. The researchers does not inject personal opinion.
However, because it is qualitative research, you can divulge in the paper that you are a school head, and that this status informs your perceptions about the data collected. Your perspective may affect how you present your discussion, but your opinions must always be with respect to the data collected from your participants, not your own experiences and beliefs outside the data.