Eye-trackers (wearable, e.g. SMI ETG2) are good tools to measure stress, if they collect pupil diameter.

Article Automatic Quantification Of Pupil Dilation Under Stress

This may seem tangential to your enquiry but it may be an area worth looking into.  There is a growing body of evidence about the impact of hte designed environment on our wellbeing.  The two areas which are most frequently researched are hospitals and schools.  This is primarily because they offer repeatable field study conditions and have many recognised measures of the performance of the people who live and work in them.  It may be more significant than you think at first glance.  My main field is in hospitals and the data today suggests that if we applied all the understood principles to a design the cost benefits from enhaced and speedier patient recovery that the cost of the new hospital could be recovered in less than five years.  We dont yet have such firm data on schools but all teh work so far suggests something similar.  My latest paper on this is jointly authoured with a colleague who specialises in schools and appears as the latest publication in my list here.  It is a chapter in a new book and is called The Quality of Place and Wellbeing.

Thank you for the answers

@ Magdalena Borys - I find it a little invasive method.

@ Bryan R Lawson - The issue you raised it could be subject of a new question: There is a correlation between stress and well-being? (Negative correlation, of course). I don't think it could be.

Some existing teacher survey instruments include stress as one of the components / constructs measured.

For example:

http://epm.sagepub.com/content/48/2/497.short

Being a pastor in addition to a teacher I ma fair game for burnout. Pastors deal with the subject enough alone. But teachers are likewise faced with the challenge of combating burnout. The number one thing I believe is an essential tool for this stress encountered by educators is to find something wholesome and productive to curtail this stress. We have to understand that despite the fact teaching is our calling, profession, and passion we can be consumed by it because there are other areas of importance in our lives. To be a productive educator we must be productive persons.

You can use of these standardised tests.

For something a little different, you could use the Sense of Coherence Scale (Antonovsky,1979) in a pre and post questionnaire.

I would start with the attachment below to garner what I could from what other scholars recommend. Because the issue of stress is cross-sectional, I would also look into how other helping professionals cope. I actually use a process to measure levels of stress on a five stage continuum: 1. Total well-being. 2. Stress (normal). 3. Problem (starting to show ware and tear). 4. Crisis (intervention/EAP recommended. 5. Burnout (disability compensation and treatment required). This method has afforded others a way to measure and intervene before levels reach the B/O stage. In the meantime I humbly recommend a publication by  Tubsing &Tubsing (1986) Vol. 3 Structured Exercises in Stress Management: A Whole Person Handbook for Trainers, Educaters and Group Leaders. Duluth, MN:  Whole Person Press.  Hope this helps to answer your question.

@Katrina McChesney and @Bhupendra Singh: Thanks for the titles, Those are useful for our research.

@ Amber S Makaiau - SOC (salutogenic concept sense of coherence ) is too much for our research because I think we can not associate stress with mental health

@ Cassandra j. williams-hemby - The five stage represent an interesting approach. However we hope in our research to find teacher only from first 3 stages. 

@ J. D. - some of the things you write are good for our research, The proposal that implies medical instruments is outside of our area of research. 

Thank you. All the responses are usefull for us in achieving a good experimental design

The following work reaches a system of actions that improves the preparation for the self-care of the health of the teachers, knowledge area where there are no updated proposals to carry out the quality jumps that are required, at least in the context that was analyzed.

The results presented in the research report have the generic name of: "Preparation for self-care of health: study and intervention in teachers, and is adopted in response to the difference that exists objectively between the whole and the parties.

Among other aspects, the issue of stress is worked with special care.

Chapter Methodological process to diagnose self-care of the teacher's health