ABSTRAKTujuan dalam penelitian ini adalah untuk: (1) menghasilkan instrumenmodel testlet sebagai instrumen pendeteksi kesulitan belajar kimia peserta didikkelas X SMA sesuai tahapan penelitian pengembangan; (2) menentukankarakteristik butir soal instrumen pendeteksi kesulitan belajar kimia kelas Xmenggunakan model testlet; (3) mendapatkan profil belajar individu peserta didikuntuk mendeteksi kesulitan belajar kimia peserta didik.Penelitian ini merupakan penelitian dan pengembangan model Akkerdengan tahapan: (1) pemeriksaan pendahuluan (preliminary investigation); (2)penyesuaian teoritis (theoretical embedding); (3) uji empiris (empirical testing);dan (4) proses dan hasil: dokumentasi, analisis dan refleksi (documentation,analysis, and reflection on process and outcome). Teknik analisis data yangdigunakan adalah deskriptif kualitatif dan kuantitatif. Data kualitatif diperolehdari: (1) validasi oleh tim ahli yaitu guru mata pelajaran kimia dan dosen ProgramStudi Pendidikan Kimia FKIP UNS; (2) uji coba skala terbatas dengan subjekpeserta didik kelas XI IPA SMA Negeri 2, SMA Negeri 5, dan SMA Batik 2Surakarta; dan (3) angket respon guru terhadap program profil belajar individupeserta didik. Data kuantitatif yang diperoleh dari uji coba skala luas dengansubjek peserta didik kelas X SMA Negeri 2, SMA Negeri 5, dan SMA Batik 2Surakarta digunakan untuk menentukan karakteristik butir soal.Berdasarkan hasil penelitian dapat disimpulkan bahwa: (1) penelitian inimenghasilkan instrumen pendeteksi kesulitan belajar kimia kelas X menggunakanmodel testlet pada bab Struktur Atom dan Sistem Periodik Unsur yang terdiri daributir soal dan program analisis datanya; (2) karakteristik butir soal instrumenpendeteksi kesulitan belajar kimia kelas X model testlet memiliki validitas isiAiken dengan rentang 0,76-1 yang berarti soal memiliki validitas isi baik;reliabilitas sebesar 0,83 yang berarti soal memiliki reliabilitas tinggi; persentasesoal dengan daya beda baik sekali sebesar 47,91%, baik 12,5%, cukup 18,75%,jelek 20,83%; persentase soal dengan tingkat kesukaran sukar 4,17%, sedang50%, mudah 45,83%; kunci jawaban 70,83% efektif; dan 93,75% butir soal sudahmemiliki pengecoh yang efektif. (3) profil belajar individu peserta didik dapatmemberi laporan yang informatif mengenai kemampuan dan kesulitan belajarkimia peserta didik.Kata Kunci: Penelitian Pengembangan, Kesulitan Belajar Kimia, Testlet, StrukturAtom dan Sistem Periodik Unsur, Profil Belajar.ABSTRACTThe aims of this research were to: (1) produce a testlet models instrumentas learning difficulties diagnostic instrument in chemistry for tenth high schoolaccording to the stages of research development. (2) determine the characteristicsof the diagnostic instrument items for learning difficulties in chemistry for tenthgrade high school using testlet models. (3) get the individual learning profile ofstudents to diagnose learning difficulties in chemistry.This research was a research and development which was developed usingAkker models with the following stages: (1) preliminary investigation; (2)theoretical embedding; (3) empirical testing; and (4) documentation, analysis, andreflection on process and outcome. The data analysis technique was descriptivequalitative and quantitative. The qualitative data were obtained from: (1)validation by a team of experts which consist of high school chemistry teachersand lecturers of Chemical Education at Sebelas Maret University (UNS); (2)limited scale trial with the students of eleventh sience program in SMAN 2,SMAN 5, and SMA Batik 2 Surakarta as the subjects; and (3) questionnaire ofteachers responses to program of student’s individual learning profile.Quantitative data were obtained from large-scale trial with the students of tenthclass SMAN 2, SMAN 5 and SMA Batik 2 Surakarta as the subjects were used todetermine the characteristics of the items.Based on the results of this study, it can be concluded that: (1) thisresearch produces diagnostic instrument of learning difficulties in chemistry fortenth grade high school using testlet models at Atomic Structure and Elements ofthe Periodic System chapter that consist of the test items and data analysisprograms. (2) items characteristics has Aiken’s content validity with a range of0.76 to 1, which means that items have good content validity; the reliability of0.83, which means that items have high reliability coefficient; the percentageabout discriminating power: excellent 47.91%, 12.5% good, fairly 18.75%,20.83% poor; the percentage about difficulty index: difficult 4.17%, medium50%, easy 45.83%; key effectiveness 70,83% and 93,75% items have effectivedistractors. (3) the student’s individual learning profile can provide informativereport about the ability and learning difficulty in chemistry.Key Words: research and development, RnD, learning difficulties, Testlet,Atomic Structure and Elements of the Periodic System.