The design and validation of a classroom observation instrument to provide formative feedback for teachers of EFL in Spain is the overarching purpose of this study. This study proposes that a valid and reliable classroom observation instrument, based on effective practice in teaching EFL, can be developed and used in Spain to enable teachers to move from where they are in their actual teaching performance to an improved level of performance. This instrument is intended to be used as part of the teachers' professional development and for formative purposes. Few instruments have been developed to assess effective practices in EFL/ESL instruction and none have been developed for use in Spain. The issues investigated through this study concerned the extent to which the observation and evaluation instrument is both valid and reliable. However, there are certain conclusions that may be drawn for each of the research questions posed. Some of the significant conclusions reached in this study were: (a) a majority of the items included in the final survey are associated with effective EFL teaching practices and are valid for use in an observation instrument; (b) this instrument can help educators, supervisors as well as cooperating teachers provide teachers with formative evaluation on their teaching behaviors in EFL instruction; (c) the instrument developed in this study exhibits appropriate content, as determined by a panel of experts; (d) construct validity was determined by internal consistency of the items using exploratory factor analysis; (e) the items that will comprise the observation instrument were shown to have reliability as well as stability; and (f) the instrument can be used by educators, supervisors, or teachers with relative ease and high degree of reliability. Some recommendations will be important to pursue: (a) conduct a inter-rater reliability study by the actual use of the instrument observing EFL teachers, (b) design a training course for the observers, and (c) conduct a longitudinal study to assure formative evaluation as a strategy for teachers professional development. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]