Penelitian ini dilakukan dengan menggunakan pendekatan penelitian pengembangan (Research and Developmen) yang langkah-langkahnya diadaptasi dari model spiral. àInstrumen penilaian unjuk kerja (performance assessment) yang àdikembangkan terdiri atas: (1) butir tugas (task); (2) audio iringan musik; (3) rubrik penilaian; (4) lembar pengamatan; dan (5) pedoman interpretasi hasil penilaian. Pengembangan indikator instrumen penilaian unjuk kerja kompetensi ekspresi dan kreasi musik dilakukan dengan mengacu pada kurikulum pembelajaran seni musik kelas IX sekolah menengah pertama (SMP). Khususnya pada standar kompetensi (SK) mengekspresikan diri melalui karya seni musik dan kompetensi dasar (KD): (1) mengaransir lagu mancanegara di Asia; dan (2) menampilkan hasil aransemen lagu mancanegara di Asia. Untuk menilai kompetensi siswa dalam mencipta melodi lagu bertangga nada diatonik mayor digunakan penilaian unjuk kerja dengan teknik uji praktik mencipta melodi lagu yang dilakukan secara tertulis. Berdasarkan hasil uji coba yang dilakukan pada tahap penerapan model menunjukkan bahwa, secara teknis model penilaian unjuk kerja kompetensi ekspresi dan kreasi musik yang dikembangkan dapat diterapkan dengan baik. Berdasarkan hasil analisis uji reliabilitas yang dilakukan dengan menggunakan analisis koefisien korelasi antarkelas (intraclass correlation coefficients/ ICC) tipe consistency definition dan tipe absolute agreement definition menunjukkan pula bahwa instrumen penilaian yang dikembangkan telah memenuhi kriteria yang ditetapkan.àThis research was conducted by using research and development approach, in which the stages were adapted out of spiral model. Performance assessment consists of (1) task; (2) audio music; (3) assessment rubric; (4) observation sheet; and (5) guidelines of assessment interpretation. Development of performance assessment indicator of expression competence and music creation was conducted by referring to music learning curriculum of junior high schools of the IX class. Especially in terms of competence standard, it means to express oneself through works of art and basic competence: (1) arrange foreign songs in Asia; and (2) perform the songââ¬â¢s arrangement in Asia. To evaluate studentsââ¬â¢ competence in creating song melody of major diatonic tone, they use performance assessment by field exam in a written way. Based on the trial conducted in the model application stage, it shows that technically the performance assessment model of expression competence and music creation could be applied well. Based on the analysis of reliability test by means of intraclass correlation coefficients/ICC of consistency definition and absolute agreement definition types, it shows that assessment instruments have fulfilled the required criteria.